1. Field of the Invention
This invention relates to onboard diagnostics of vehicle operating parameters.
2. Prior Art
It is known to use oxygen sensors in the feedback control of air/fuel ratio of internal combustion engines. It is desirable to know when there has been a failure of an oxygen sensor or of the air/fuel ratio control system. It would be generally expected that throttle position transitions due to a vehicle operator actuation would result in exhaust gas oxygen sensor output level switching. Accordingly, it is known to monitor the number of throttle position transitions and compare it to a predetermined number of throttle position transitions. If the actual number of throttle position transitions is greater than the predetermined number, a transition in the output level of an exhaust gas oxygen sensor would be expected. If no such switching or output level transition of the oxygen sensor has occurred, it is assumed that there is some incorrect operation of the fuel control system, such as, for example, exhaust gas oxygen sensor failure.
However, this is only an approximate determination of a fault. For example, there may well be other failure modes which cannot be detected by such a simplistic method. These are some of the problems this invention overcomes.